1. Field of the Invention
The present invention relates generally to nerve stimulation or neuromodulation and more particularly to implantable nerve stimulation or neuromodulation systems and methods.
2. Description of the Related Art
Urinary incontinence is a symptom that can be caused by a wide variety of conditions. Some urinary incontinence conditions are temporary and may result from urinary tract or vaginal infections, constipation, or the effects of medicine, including such medicines as diuretics, antidepressants and other drugs causing anticholinergic effects, as well as sedatives, narcotics, analgesics, etc. which can cause muscle relaxation, sedation, delirium, and/or immobility. Other urinary incontinence conditions are longer-lasting, and may even be permanent. Such longer lasting incontinence conditions may be caused by obesity, pregnancy and vaginal child birth, pelvic surgeries such as hysterectomies, trauma resulting in damage to the nerves that control the bladder, stroke, and chronic diseases that cause nerve and bladder neuropathy such as multiple sclerosis, diabetes and Parkinson's disease.
Incontinence is classified by the symptoms or circumstances occurring at the time of the urine leakage. Stress incontinence is a term used to refer to loss of bladder control resulting from poor bladder support by the pelvic muscles or by weak or damaged sphincter muscles. This condition allows urine to leak when the abdomen is stressed or strained, such as during coughing, sneezing, laughing, bending over and even walking. Urge incontinence results when the bladder contracts unexpectedly causing urine leakage. An overactive bladder may result from infection that irritates the bladder lining, nerve damage, and other conditions. Mixed incontinence is often a combination of both stress incontinence and urge incontinence. Overflow incontinence occurs when the bladder is allowed to become so full that it simply overflows. This happens when bladder weakness or a blocked urethra prevents normal emptying of the bladder. An enlarged prostate can result in such blockage. For this reason, overflow incontinence is more common in men that in women. Bladder weakness can develop in both men and women, but it happens most often in people with diabetes, heavy alcohol users, and others with decreased nerve function.
Overactive bladder (“OAB”) is a combination of symptoms including urgency (the strong need to urinate), frequency (repetitive need to void) and/or urge incontinence. OAB is highly correlated with age and, for women, childbirth. OAB causes embarrassment to patients and very often negatively affects their social and sex lives. In the past, accurate data on the prevalence of OAB was unavailable partly due to the unwillingness of patients to discuss their symptoms and the market's common belief that there were no treatments. Recent epidemiological studies, however, have provided data on the prevalence of OAB symptoms in the adult population grouped according to age and gender. According to these studies 19.6 million Americans experience OAB and the incidences of OAB are projected to climb to 24.2 million by 2015. Researchers overwhelmingly report that these estimates could grossly underestimate those affected as women commonly accept OAB, secondary to childbirth, as something “to live with.” Further, it is known that those affected are hesitant to discuss their symptoms with doctors as they are embarrassed by their condition and have been discouraged by the lack of solutions. As a result, less conservative studies estimate that OAB currently affects 53 million Americans.
To understand the causes of (“OAB”) and the ability to treat OAB through nerve stimulation or neuromodulation, it is necessary to have a proper understanding of the urinary system and its operation.
Urine comprises waste and water removed from the blood by the kidneys. Urine flows from the kidneys downward through a pair of tubes, the ureters, to the bladder. The bladder is a balloon-like container that stores urine. Urine leaves the body through another tube, the urethra, at the bottom of the bladder.
The act of urinating is controlled by muscles that comprise the outflow controls, called sphincters, located at the base of the bladder and in the wall of the urethra, referred to as the detrusor muscles. In a healthy or normal urinary system, the sphincter muscles are constantly in a state of active contraction, except during the voluntary act of evacuation. Thus, in the contracted state, the contracted sphincter muscles close-off the neck of the bladder and the urethra, much like a tie at the base of a balloon, to prevent the flow of urine from the bladder. During urination, the sphincter muscles are relaxed thereby causing the neck of the bladder and the urethra to open. At the same time, the detrusor muscle contracts to squeeze the bladder thereby forcing the urine to evacuate the bladder. When the bladder is empty and urination is completed, the detrusor muscle returns to its normal relaxed state and the sphincter muscles again return to their normally contracted state, to close-off the neck of the bladder and urethra to prevent any further passage of urine from the bladder.
It is well known that electrical stimulation of the S2 and S3 sacral nerves can modulate the neuromuscular control of bladder function in a human. The S2 sacral nerve constitutes the main motor supply to the external sphincter muscle. Whereas the S3 sacral nerve constitutes the main motor supply to the detrusor muscle. It is also known that electrical stimulation of the tibial nerve at approximately two inches (5 cm) cephalic to the medial tibial malleolus, can stimulate the S2 and S3 sacral nerves, thereby enabling modulation of the bladder, in substantially the same way as if directly stimulating the S2 and S3 sacral nerves. Thus, modulation of the tibial nerve provides a less invasive and less costly method of achieving the same, if not better results, than the highly invasive spinal, abdominal or genito-pelvic implants which are more difficult to place, present a greater likelihood of complications, and necessarily involve higher costs.
Accordingly, there is a need for a nerve stimulation or neuromodulation system that is less invasive when compared to other neurostimulation implant procedures so as to minimize risk of complications and which is easier and less time consuming for the physician to place in the patient, but which is effective for both nerve and muscle stimulation for treatment of numerous conditions, including, but not limited to, urge incontinence, urinary frequency, non-obstructive urinary retention and interstitial cystitis, as well as for treating chronic pain, Parkinson's disease, multiple sclerosis and other neuromuscular disorders and for general muscle and joint rehabilitation.